Systems and methods for shielding current transducers

ABSTRACT

A shield for protecting a current transducer from noise may include a first annular ring that may be disposed adjacent to a first side of a current sensor. The shield may also include a second annular ring that may be disposed adjacent to a second side of the current sensor opposite the first side, such that the first and second annular rings each include magnetically permeable material.

BACKGROUND

The subject matter disclosed herein relates to systems and method forcalibrating current transducers. More specifically, the subject matterdisclosed herein relates to calibrating phase and sensitivitycharacteristics of a current transducer output.

A current transducer generally includes a winding around a magneticcore. When the current transducer is placed around a cable or other typeof conductor, a time-varying (e.g., alternating current) currentconducting through the cable may produce a time-varying magnetic fieldin the magnetic core. The magnetic field may then induce a current inthe winding of the current transducer. The current in the winding may beproportional to the current conducting through the cable. As such, thecurrent in the winding may be used to measure a magnitude and directionof the current conducting in the cable.

However, conventional current transducers have relatively hightolerances in their electrical (i.e., resistance) and magnetic (i.e.,inductance) characteristics due to magnetic properties of the materialsinside the current transducers and the manufacturing process used tocreate the current transducers. That is, each current transducer mayhave its own sensitivity or tolerance levels based on its inherentcharacteristics. These sensitivity levels produce a higher degree ofuncertainty in an electrical signal output by each current transducer.Additionally, these inherent characteristics may also introduce a phaseshift between the signal output by the current transducer and a measuredcurrent. Accordingly, it would be beneficial to calibrate currenttransducers to perform at specified or known tolerance levels, and phaseshifts.

Moreover, conventional current transducers use a steel tape to shieldinternal components, such as a current sensor, against various types ofnoise (e.g., electrical or magnetic noise). That is, the steel tape maybe wound around a piece of metal to form a shield that may be placedaround the current sensor. Using four steel tape-wound shields, eachside of the current sensor may be shielded against magnetic disturbancesand noise. However, creating each steel tape-wound shield is a complexprocess that may easily be mishandled, thereby jeopardizing theintegrity of the overall shield around the current sensor. Accordingly,it would be beneficial to provide a more easily manufactured apparatusfor shielding the components inside the current transducer.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the original claims aresummarized below. These embodiments are not intended to limit the scopeof the claims, but rather these embodiments are intended only to providea brief summary of possible forms of the presently disclosed systems andtechniques. Indeed, the claims may encompass a variety of forms that maybe similar to or different from the embodiments set forth below.

In one embodiment, a shield for protecting a current transducer fromnoise may include a first annular ring that may be disposed adjacent toa first side of a current sensor. The shield may also include a secondannular ring that may be disposed adjacent to a second side of thecurrent sensor opposite the first side, such that the first and secondannular rings each include magnetically permeable material.

In another embodiment, a system may include a housing having a firstcavity and a second cavity, a current sensor disposed in the firstcavity, a calibration circuit disposed in the second cavity, and a setof shields disposed within the housing about the current sensor. The setof shields may include first and second shields disposed on axiallyopposite sides of the current sensor, and third and fourth shieldsdisposed on radially opposite sides of the current sensor.

In yet another embodiment, a method of operation for a solid-side shieldmay include absorbing electrical and/or magnetic interference with a setof shields disposed about a current sensor, such that the set of shieldsmay include first and second shields disposed on axially opposite sidesof the current sensor. The first and second shields may be composed ofmagnetically permeable material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic diagram illustrating an embodiment of a currenttransducer calibration system, in accordance with aspects of the presentdisclosure;

FIG. 2 illustrates an embodiment of a calibration circuit in the currenttransducer calibration system of FIG. 1, in accordance with aspects ofthe present disclosure;

FIG. 3 is a flow chart illustrating an embodiment of a method forcalibrating a current transducer using the current transducercalibration system of FIG. 1, in accordance with aspects of the presentdisclosure;

FIG. 4 illustrates a top perspective view of an embodiment of a housingfor a shield to shield a current transducer in the current transducercalibration system of FIG. 1, in accordance with aspects of the presentdisclosure;

FIG. 5 illustrates an inside view of an embodiment of the housing ofFIG. 4, in accordance with aspects of the present disclosure;

FIG. 6 illustrates an exploded view of an embodiment of the shield ofFIG. 4, in accordance with aspects of the present disclosure;

FIG. 7 illustrates a top view of a square-shaped embodiment of theshield of FIG. 4, in accordance with aspects of the present disclosure;

FIG. 8 illustrates a top view of a octagonal-shaped embodiment of theshield of FIG. 4, in accordance with aspects of the present disclosure;and

FIG. 9 illustrates a top view of a hexagonal-shaped embodiment of theshield of FIG. 4, in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, not all featuresof an actual implementation are described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

Current transducers may be used for a variety of purposes includingmeasuring an actual current input and/or output of a device (e.g.,generator, motor), determining an amount of leakage current within thedevice, or the like. One challenging application of a current transducermay include accurately measuring the leakage current of stator windingsof a motor or generator in real-time. Leakage current is a complexsignal that includes an amplitude and phase (i.e., relative to themotor's or generator's line voltage) having a real (i.e., resistive)component and an imaginary (i.e., capacitive) component. Moreover, theleakage current's signal level is generally very low as compared to thesignal of the motor's line current. Therefore, an accurately calibratedcurrent transducer would be beneficial for acquiring this measurement.

Keeping this in mind, embodiments of the present disclosure generallyrelate to a calibration circuit and methods for using the calibrationcircuit to calibrate different current transducers, such that eachtransducer may have similar sensitivity and phase characteristics in itsmeasurements. In one embodiment, the calibration circuit may include twovariable resistors connected in series. Here, the first variableresistor may be used to adjust the sensitivity of the measurement outputof the current transducer, while the second variable resistor may beused to adjust the phase shift of the measurement output. By controllingthe sensitivity and the phase shift of the measurement output of eachcurrent transducer, the calibration circuit may enable each currenttransducer to be calibrated to certain specifications, thereby creatinguniformity between each manufactured current transducer and improvingdata quality for the measurements acquired by each calibrated currenttransducer.

In addition to providing systems and methods for calibrating currenttransducers, embodiments of the present disclosure also generally relateto a solid-side shield that may be coupled on the sides of a currentsensor within the current transducer. The solid-side shield may protectthe current sensor from various types of noise that may affect themeasurement output of the current transducer. Keeping this in mind, inone embodiment, the solid-side shield may be fabricated to form fourannular rings that may fit within a housing that may be used to shieldeach side of the current sensor. The annular rings may be composed of amagnetically permeable material and may be combined to fit preciselyaround each axial side of the current sensor. The annular rings may befabricated to precise dimensions using a laser, a water jet, or thelike. Since the annular rings may be fabricated to form a shieldingbarrier around each axial side of the current sensor, the solid-sideshield may be capable of providing improved shielding as compared tousing a traditional steel tape wound shield.

By way of introduction, FIG. 1 depicts a schematic diagram of a currenttransducer calibration system (current transducer 10). The currenttransducer 10 may include a current sensor 12 and a calibration circuit14. The current sensor 12 may be a current transformer that employs atoroidal inductor and a ferrite core to sense a coupling magnetic fieldfrom an electric current conducting through a conductor. The calibrationcircuit 14 may be used to calibrate the measurement output of thecurrent transducer 10.

In one embodiment, the current sensor 12 may be coupled around aconductor 16, which may conduct current I. Here, the toroidal inductormay produce a current or voltage output (i.e., measurement output of thecurrent sensor 12) that is proportional to the amplitude of the currentI. Although FIG. 1 depicts the current sensor 12 as being coupled arounda single conductor 16, it should be noted that the current sensor 12 maybe coupled around multiple conductors. As such, the current sensor 12may measure the net current with respect to all of the conductors beingmonitored by the current sensor 12.

Generally, the measurement output of the current sensor 12 (i.e., themeasurement output of the current transducer 10) may include a phaseshift (e.g., degrees) between the measurement output and the current I.The amount of the phase shift may depend on the intrinsic inductance,capacitance, and/or resistance within the current transducer 10 (i.e.,within the current sensor 12 and the calibration circuit 14) and animpedance of any load circuit coupled to the current transducer 10.Moreover, since each individual current transducer 10 may have differentintrinsic inductance, capacitance, and/or resistance properties, eachcurrent transducer 10 may have different sensitivities or tolerances.That is, each current transducer 10 may output a slightly differentmeasurement value for the same input current due to the differentsensitivities of each current transducer 10. For example, one currenttransducer 10 may output 1 volt when 100 amps of current are conductingvia the conductor 16 while another current transducer 10 may output 1.1volts when the same 100 amps of current are conducting via the conductor16. The sensitivity of each current transducer 10 may vary due to avariety of factors including a number of winding turns on the toroidalinductor, an intrinsic resistance of the toroidal inductor, theresistance of a load circuit, and the like.

Keeping the foregoing in mind, the calibration circuit 14 may controlthe phase shift and/or the sensitivity properties of the currenttransducer 10. That is, the calibration circuit 14 may adjust the phaseshift and/or the sensitivity properties of the output of the currenttransducer 10 to match some desired phase shift and/or sensitivityproperty. In one embodiment, the calibration circuit 14 may be used tocalibrate different current transducers 10, such that the measurementoutput for each current transducer 10 may be substantially similar orequal (e.g., less than 1%). For instance, the calibration circuit 14 mayadjust the phase shift and sensitivity properties of the measurementoutput of multiple current transducers 10 such that each currenttransducer 10 outputs substantially similar or equal values for variousinput currents (e.g., current I).

The calibration circuit 14 may control the phase shift and/or thesensitivity properties of the current transducer 10 by adjusting theresistances of two variable resistors in the calibration circuit 14. Forinstance, FIG. 2 illustrates a circuit diagram 20 of the currenttransducer 10 that depicts the current sensor 12 coupled to thecalibration circuit 14. As shown in FIG. 2, the calibration circuit 14includes a phase shift resistor 22 connected in series with asensitivity resistor 24, which may be used to control the phase shiftand the sensitivity properties of the measurement output of the currenttransducer 10, respectively. The phase shift resistor 22 and thesensitivity resistor 24 may be variable resistors that may be adjustedto calibrate for the phase shift and the sensitivity properties of themeasurement output of the current transducer 10. In certain embodiments,the phase shift resistor 22 and the sensitivity resistor 24 may beadjusted until the measurement output of the current transducer 10substantially matches a desired or specified measurement output value.In this manner, multiple current transducers 10, each having a differentcurrent sensor 12 and a different calibration circuit 14, may becalibrated, such that each calibrated current transducer 10 may exhibitthe same measurement properties even though each current transducer 10may have different inherent inductances, capacitances, resistances, andthe like. Moreover, if an operating current transducer 10 fails in thefield, the calibration circuit 14 may be used to calibrate a replacementcurrent transducer 10, such that the failed current transducer 10 may bereplaced with a current transducer 10 that has the same phase shift andsensitivity properties of the current transducer 10 that is beingreplaced. As such, the replacement current transducer 10 may continue toprovide a user or system with measurement data similar or equal to thatof the previously employed current transducer 10, thereby maintainingthe integrity of any subsequently collected measurement data.

In one embodiment, the calibration circuit 14 may be coupled across asecondary winding of the current sensor 12. The calibration circuit 14may also be coupled to a protection circuit 26, which may include anumber of resistors, diodes, zener diodes, and the like. The protectioncircuit 26 may protect the phase shift resistor 22, the sensitivityresistor 24, and the current transducer 10 from voltage spikes, shortcircuits, and the like. Moreover, the protection circuit 26 may protectadditional equipment connected to the current transducer 10 or thecalibration circuit 14 from excessive energy. Examples of the additionalequipment may include signal-conditioning equipment, various typed ofmonitoring devices, plant control equipment, and the like.

The calibration circuit 14 may include an output terminal 28 that maymeasure a voltage across the sensitivity resistor 24. The outputterminal 28 may correspond to the measurement output of the currenttransducer 10 and may also be used to calibrate the current transducer10. That is, the voltage waveform acquired via the output terminal 28may be used to determine whether the phase shift or the sensitivityproperties of the current transducer 10 should be adjusted to targetlevels, as provided by a user, model, table, or the like. Further, incertain embodiments, the resistances of the phase shift resistor 22 andthe sensitivity resistor 24 may each be adjusted until the voltagewaveform acquired via the output terminal 28 substantially matches adesired voltage waveform that has specified phase shift and sensitivityproperties.

As mentioned above, the measurement output of the current transducer 10may be proportional to the current I conducting through the conductor16. Keeping this in mind, the voltage waveform acquired at the outputterminal 28 is also proportional to the current I. In one embodiment,the current I may be supplied to the conductor 16 by a current source30. The current source 30 may be an accurate current source that mayprovide the current I, such that the current I may accurately reflect acurrent value as specified or input into the current source 30. In thismanner, the current transducer 10 may be accurately calibrated based ona known current value provided to the conductor 16.

Generally, the phase shift resistor 22, the sensitivity resistor 24, andthe current source 30 may be controlled and operated individually by auser/operator who may use the calibration circuit 14 to calibrate thecurrent transducer 10. However, in certain embodiments, the phase shiftresistor 22, the sensitivity resistor 24, and the current source 30 maybe coupled to a controller 32. The controller 32 may control the phaseshift resister 22, the sensitivity resistor 24, and the current source30 using a communication component 34, a processor 36, a memory 38, astorage 40, input/output (I/O) ports 42, and the like.

The communication component 34 may be a wireless or wired communicationcomponent that may facilitate communication between various components(e.g., current source 30) within the current transducer 10. Theprocessor 36 may be any type of computer processor or microprocessorcapable of executing computer-executable code. The memory 38 and thestorage 40 may be any suitable articles of manufacture that can serve astangible machine-readable media to store processor-executable code orinstructions. These articles of manufacture may representcomputer-readable media (e.g., any suitable form of memory or storage)that may store the processor-executable code executable by the processor36 to perform presently disclosed techniques.

The controller 32 may also be coupled to the output terminal 28, suchthat it may monitor the voltage waveforms output by the currenttransducer 10. In one embodiment, the controller 32 may receive phaseshift and sensitivity properties from a user and may then automaticallycalibrate the current transducer 10. That is, the controller 32 mayspecify to the current source 30 a current value to provide to theconductor 16 and may subsequently monitor the voltage waveform at theoutput terminal 28. The controller 32 may then calibrate the currenttransducer 10 by adjusting the resistances of the phase shift resistor22 and the sensitivity resistor 24 until the voltage waveform acquiredat the output terminal 28 has phase shift and sensitivity propertiesthat substantially matches the received phase shift and sensitivityproperties. Additional details with regard to a method for calibratingthe current transducer 10 using the calibration circuit 14 will bedescribed in greater detail with respect to FIG. 3 below.

FIG. 3 illustrates a flow chart of a method 50 that may be employed forcalibrating the current transducer 10 using the calibration circuit 14.In one example, the method 50 may be performed by the controller 32,however, it should be noted that the method 50 may also be performed byone or more users/operators who may control the resistances of the phaseshift resistor 22 and the sensitivity resistor 24 as well as the currentsource 30 and who may monitor the voltage output at the output terminal28.

At block 52, the controller 32 may receive an input current waveform andan expected or desired current transducer measurement output. The inputcurrent waveform may include an amplitude and frequency for a currentwaveform that represents current I, which may be supplied to theconductor 16 via the current source 30. In turn, the expected currenttransducer measurement output may correspond to an expected output valueassociated with the input current waveform for the current I conductingthrough the conductor 16 in the current transducer 10. Moreover, thecurrent transducer measurement output may also specify a particularphase shift at which a waveform for the current transducer measurementoutput may shift from the waveform of the provided current I.

After receiving these values, at block 54, the controller 32 may send asignal to the current source 30 to provide the conductor 16 with thecurrent I that corresponds to the input current waveform received atblock 52. The current source 30 may then supply the conductor 16 withthe appropriate current I.

At block 56, the controller 32 may receive the current transducermeasurement output via the output terminal 28. In one embodiment, thecontroller 32 may receive a voltage waveform that may be proportional toa current waveform associated with the current I conducting through theconductor 16.

Using the expected current transducer measurement output received atblock 52 and the actual current transducer measurement output receivedat block 56, the controller 32, at block 58, may determine whether theactual current transducer measurement output substantially matches theexpected current transducer measurement output. For instance, thecontroller 32 may determine whether the amplitude of the actual voltagewaveform matches the amplitude of the expected voltage waveform withinthe same degree or tolerance (e.g., less than 1%). Moreover, thecontroller 32 may also determine whether the actual voltage waveform isin phase with the expected voltage waveform. If either the amplitude ofthe actual voltage waveform does not match the amplitude of the expectedvoltage waveform or if the actual voltage waveform is not in phase withthe expected voltage waveform, the controller 32 may proceed to block60.

At block 60, the controller 32 may send a signal to the phase shiftresistor 22, the sensitivity resistor 24, or both, to adjust theirrespective resistances such that the amplitude and the phase of theactual voltage waveform acquired at the output terminal 28 matches theamplitude and the phase of the expected voltage waveform. In oneembodiment, the controller 32 may adjust the resistances of the phaseshift resistor 22 and the sensitivity resistor 24 according to thetransfer function of Equation 1, as shown below:

$\begin{matrix}{\frac{\overset{\_}{V_{o}}}{\overset{\_}{I_{t}}} = {\frac{N_{p}}{N_{s}}\left\lbrack {\frac{\omega^{2}L_{m}^{2}R_{L}}{\left( {R_{S} + R_{F} + R_{L}} \right)^{2} + \left( {\omega\; L_{m}} \right)^{2}} + \frac{{j\omega}\; L_{m}{R_{L}\left( {R_{S} + R_{F} + R_{L}} \right)}}{\left( {R_{S} + R_{F} + R_{L}} \right)^{2} + \left( {\omega\; L_{m}} \right)^{2}}} \right\rbrack}} & (1)\end{matrix}$where V_(o) corresponds to the actual voltage acquired at the outputterminal 28, I_(t) corresponds to the current I conducting via theconductor 16, N_(p) corresponds to the number of primary windings in thecurrent transducer calibration system 10, N_(s) corresponds to thenumber of secondary winding in the current transducer 12, ω correspondsto the angular frequency of the current I, L_(m) corresponds to theinductance of the current transducer 12, R_(s) corresponds to theresistance of the windings in the current transducer 12, R_(F)corresponds to the resistance of the phase shift resistor 22, and R_(L)corresponds to the sensitivity resistor 24.

Moreover, the phase angle may be characterized according to Equation 2,as shown below:

$\begin{matrix}{{\theta\left( {{phase}\mspace{14mu}{angle}} \right)} = {{Arctan}\left( \frac{R_{S} + R_{F} + R_{L}}{\omega\; L_{m}} \right)}} & (2)\end{matrix}$

As such, the controller 32 may adjust the resistances of the phase shiftresistor 22 and the sensitivity resistor 24 based on the actual voltageacquired via the output terminal 28 and Equations 1 and 2. Afterwards,the controller 32 may then proceed back to block 56 and receive anupdated current transducer measurement output and continuously performblocks 56, 58, and 60 until the actual voltage waveform acquired via theoutput terminal 28 substantially matches the expected voltage waveform(e.g., less than 1% difference). As such, the controller 32 may adjustthe resistances of the phase shift resistor 22 and the sensitivityresistor 24 until the actual voltage waveform substantially matches theexpected voltage waveform.

Referring back to block 58, when the actual voltage waveform matches theexpected voltage waveform, the controller 32 may proceed to block 62 andend the method 50. That is, since the actual voltage waveform matchesthe expected voltage waveform at block 62, the current transducer 10 maybe considered calibrated as per the parameters received at block 52. Incertain embodiments, the method 50 may be performed on a number ofcurrent transducers soon after being manufactured. As such, each of themanufactured current transducers may exhibit substantially similar phaseshift and sensitivity properties. As a result, current transducers maybe manufactured using lower cost components (e.g., interchangeable)since their effects to the capacitance, inductance, and the resistanceof the current transducer may be compensated for using the calibrationcircuit 14.

Further, as mentioned above, one challenging aspect related to using thecurrent transducer 10 may include accurately measuring a leakage currentof stator windings of a motor or generator in real-time. Excessiveleakage current in the stator windings may cause damage to the motor orgenerator. However, leakage current is a complex signal that includes anamplitude and phase (i.e., relative to motor's line voltage) and real(e.g., resistive) and imaginary (e.g., capacitive) components, and itssignal level may be very low as compared to the signal of the motor'sline current. Therefore, a current sensor with high accuracy andperformance may be useful in consistently acquiring accurate leakagecurrent measurements.

By employing the calibration circuit 14 described above, a number ofsimilarly designed current transducers may consistently output similaror equal measurement values for the same input currents. That is, thecalibration circuit 14 may calibrate different toroidal-type currenttransducers 10 that may have high tolerance levels in their electrical(e.g., resistance) and magnetic (e.g., inductance) properties due to themagnetic properties of the materials and manufacturing process used tocreate them. Moreover, the calibration circuit 14 may compensate for aphase shift between an output signal of the current transducer 10 and ameasured leakage current. Therefore, the calibration circuit 14described above may enable current transducers 10 to be manufacturedwith a much larger variation in component specifications. As a result,the manufacturing cost related to producing the current transducer maydecrease and each current transducer 10 may be calibrated to meet morestringent performance specifications.

In addition to using the calibration circuit 14 to manufacture currenttransducers 10 having similar output measurement values, a solid-sideshield may be used to consistently shield each manufactured currenttransducer 10. As mentioned above, traditional tape-wound shields maynot be manufactured consistently due to the complexity of themanufacturing process. As such, each current transducer 10 shieldedusing a tape-wound shield may be affected by electrical and magneticnoise differently, thereby affecting the measurement output of eachcurrent transducer 10 differently.

Keeping this in mind FIG. 4 illustrates a top perspective view of asolid-side shield assembly 70. The solid-side shield assembly 70, in oneembodiment, may include a housing 72 that may generally form an annularshape 73 and may include an annular cavity 74 that may fit amagnetically permeable material used to shield the current transducer10. The magnetically permeable material may absorb magnetic fields. Incertain embodiments, the magnetically permeable material is such thatits permeability may be measured with respect to free space.

The housing 72 may be composed of plastic, aluminum, any polymer,fiberglass, non-ferrite metals, or the like. In one embodiment, thehousing 72 may include an extended cavity 76 that may enclose thecalibration circuit 14. As such, the housing 72 may also includeconnector pins 78 that may be used to provide access to the outputterminal 28 of the calibration circuit 14, which may enable a user tocalibrate the current transducer 10 via the calibration circuit 14.

Keeping this in mind, FIG. 5 illustrates the annular cavity 74 and theextended cavity 76 from an inside view 80 of the housing 72. The housing72 may include a base 73, an inner annular cavity wall 75 and an outerannular cavity wall 77. As such, the annular cavity 74 may encompass thespace between the base 73, the inner annular cavity wall 75, and theouter annular cavity wall 77. Generally, the housing 72 may be formed,such that the base 73, the inner annular cavity wall 75, and the outerannular cavity wall 77 may be composed of the same material and formedfrom one piece of that material. In one embodiment, the calibrationcircuit 14 may fit inside the outer annular cavity wall 77 within theextended cavity 76, such that it may be accessed via connector pins 78,which may enable wires, cables, and the like access to the calibrationcircuit 14.

As mentioned above, the annular cavity 74 may fit four annular rings,such that each annular ring may shield one side of the current sensor12. FIG. 6 illustrates a cross-sectional exploded view 90 of thesolid-side shield assembly 70 cut vertically down line I in FIG. 4. Assuch, FIG. 6 depicts how each annular ring may fit around the currentsensor 12. As shown in FIG. 6, the solid-side shield assembly 70 mayinclude an inner annular ring 92 (e.g., radially inner ring or disc), anouter annular ring 94 (e.g., radially outer ring or disc), a top sideannular ring 96 (e.g., axially upper ring or disc), and a bottom sideannular ring 98 (e.g., axially lower ring or disc). As such, the innerannular ring 92 and the outer annular ring 94 may be radially spacedapart from one another, and the top side annular ring 96 and the bottomside annular ring 98 may be axially spaced apart from one another.Additionally, the inner annular ring 92 and the outer annular ring 94may be concentric with one another.

In one embodiment, a radial distance D between the inner and outer radiiof the top side annular ring 96 and the bottom side annular ring 98 maybe approximately equal to or greater than a radial thickness T1 of theinner annular ring 92 plus a radial thickness T2 of the current sensor12 plus a radial thickness T3 of the outer annular ring 94. As such, thetop side annular ring 96 and the bottom side annular ring 98 mayeffectively shield the top and bottom portions of the current sensor 12from electrical or magnetic noise that may be present outside thehousing 72.

Referring back to the inner annular ring 92 and the outer annular ring94, a length L1 (e.g., axial height) of the inner annular ring 92 and alength L3 (e.g., axial height) of the outer annular ring 94 may beapproximately equal to or greater than the length L2 (e.g., axialheight) of the current sensor 12. As such, the inner and outer radii ofthe current sensor 12 may be effectively shielded from electrical ormagnetic noise that may be present outside the housing 72. Incombination, the inner annular ring 92, the outer annular ring 94, thetop side annular ring 96, and the bottom side annular ring 98 may shieldeach side of the current sensor 12, such that the entire current sensor12 is effectively shielded from various magnetic and electrical noisesources.

Although the solid-side shield assembly 70 has been described as havingfour annular rings, it should be noted that the solid-side shieldassembly 70 may include just two annular rings. That is, in certainembodiments, the solid-side shield assembly 70 may include the top sideannular ring 96 and the bottom side annular ring 98 to shield the sidesof the current sensor 12 having the largest surface areas. In this case,the inner and outer annular rings may be tape-wound shields.

The housing 72 may also include a lid 100. The lid 100 may be coupled tothe inner annular cavity wall 75, the outer annular cavity wall 77, theinner annular ring 92, the outer annular ring 94, the top annular ring96, or the bottom annular ring 98 using fasteners such as screws and thelike. Once the housing 72 is fastened together using the lid 100, thesolid-side shield assembly 70 may effectively shield the currenttransducer 10 from electrical or magnetic noise that may be presentoutside the housing 72.

In certain embodiments, the inner annular ring 92, the outer annularring 94, the top annular ring 96, and the bottom annular ring 98 mayeach be composed of a magnetically permeable material, such that itspermeability may be measured with respect to free space, such as aSupermalloy (e.g., nickel-iron alloy), Metglas®, Ultraperm, MuMETAL®, orthe like. As such, the inner annular ring 92, the outer annular ring 94,the top annular ring 96, and the bottom annular ring 98 may each besolid pieces of material fabricated to precise measurements using alaser cutter, a water jet cutter, or the like. Generally, the thicknessof the inner annular ring 92, the outer annular ring 94, the top annularring 96, and the bottom annular ring 98 may be at least 0.075 inches. Incertain embodiments, the inner annular ring 92, the outer annular ring94, the top side annular ring 96, or the bottom side annular ring 98 mayinclude several pieces stacked on top of each other to form a completeinner annular ring 92, outer annular ring 94, top side annular ring 96,or bottom side annular ring 98. That is, for example, the top sideannular ring 96 may be composed of 10 0.0075 inch pieces of themagnetically permeable material stacked on top of each other to form thesingle 0.075 inch top side annular ring 96.

In certain embodiments, two or three of the inner annular ring 92, theouter annular ring 94, the top annular ring 96, and the bottom annularring 98 may be formed together as a single piece. That is, two or threeof the inner annular ring 92, the outer annular ring 94, the top annularring 96, and the bottom annular ring 98 may be fabricated from themagnetically permeable material, such that two or three of the two orthree of the inner annular ring 92, the outer annular ring 94, the topannular ring 96, and the bottom annular ring 98 are formed together. Forinstance, the inner annular ring 92 and the bottom annular ring 98 maybe fabricated from a single piece of the magnetically permeablematerial, thereby forming a first single shielding piece. In the samemanner, the outer annular ring 94 and the top annular ring 96 may befabricated from a single piece of the magnetically permeable material,thereby forming a second single shielding piece. Both of these piecesmay then be positioned around the current sensor 12, such that thecurrent sensor 12 may be shielded on each of its sides. In the samemanner, the inner annular ring 92, the outer annular ring 94, and thetop annular ring 96 may be fabricated from a single piece of themagnetically permeable material, thereby forming a single shieldingpiece that may fit around three sides of the current sensor 12. Thebottom annular ring 98 may then be positioned on top of the resultingthree-sided shielding piece to shield the current sensor 12 from noisein each direction.

Although the solid-side shield assembly 70 has been described as havingan annular-shaped housing 72, annular-shaped lid 100, and four annularshielding rings (i.e., inner annular ring 92, outer annular ring 94, topannular ring 96, and bottom annular ring 98), it should be noted thatthe solid-side shield assembly 70 may also be formed in other shapes,such that the current transducer 10 may fit within the solid-side shieldassembly 70. By way of example, the solid-side shield assembly 70 mayhave a square-shaped outer edge and an annular-shaped inner edge, asdepicted in FIG. 7. As such, the annular-shaped housing 72,annular-shaped lid 100, the outer annular ring 94, the top annular ring96, and the bottom annular ring 98, as depicted in FIG. 6, may be formedsuch that each aforementioned piece may have a square-shaped outer edgeand an annular shaped inner edge, while the inner annular ring 92 mayhave annular-shaped inner and outer edges.

In another example, the solid-side shield assembly 70 may have anoctagonal-shaped outer edge and an annular-shaped inner edge, asdepicted in FIG. 8, or a hexagonal-shaped outer edge and anannular-shaped inner edge, as depicted in FIG. 9. In this manner, theannular-shaped housing 72, annular-shaped lid 100, the outer annularring 94, the top annular ring 96, and the bottom annular ring 98, asdepicted in FIG. 6, may have outer edges formed according to the shapesof the outer edges in FIG. 8 and FIG. 9, while the inner annular ring 92may have annular-shaped inner and outer edges.

By precisely fabricating the inner annular ring 92, the outer annularring 94, the top annular ring 96, and the bottom annular ring 98 todimensions such that the current sensor 12 is completely enclosed by theshielding material, manufacturers and assemblers may consistentlyprovide the same level of shielding to each manufactured currenttransducer 10. Moreover, the inner annular ring 92, the outer annularring 94, the top annular ring 96, and the bottom annular ring 98 may beproduced and ready for assembly with the current transducer 10, therebymaking the manufacturing process for the current transducer 10 moreefficient. That is, since the calibration circuit 14, the housing 72,the lid 100, the inner annular ring 92, the outer annular ring 94, thetop annular ring 96, and the bottom annular ring 98 are each removablepieces, the assembly and repair of the current transducer 10 or thesolid-side shield assembly 70 may be more efficiently performed.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

The invention claimed is:
 1. A shield, comprising: a first annular ringconfigured to be disposed adjacent to a first side of a current sensor;a second annular ring configured to be disposed adjacent to a secondside of the current sensor opposite the first side, wherein the firstand second annular rings each comprise a magnetically permeablematerial; a third annular ring configured to be disposed adjacent to athird side of the current sensor; and a fourth annular ring configuredto be disposed adjacent to a fourth side of the current sensor oppositethe third side, wherein the first and second annular rings are axiallyspaced apart from one another, and the third and fourth annular ringsare radially spaced apart from one another, and wherein a distancebetween an inner radius and an outer radius of the first annular ringand the second annular ring is approximately equal to or greater than asum of a thickness of the third annular ring, a thickness of the currentsensor, and a thickness of the fourth annular ring.
 2. The shield ofclaim 1, wherein a distance between an inner radius and an outer radiusof the second annular ring is approximately equal to or greater than athickness of the third annular ring, a thickness of the current sensor,and a thickness of the fourth annular ring.
 3. The shield of claim 1,wherein the third and fourth annular rings are concentric with oneanother.
 4. The shield of claim 1, wherein the third and fourth annularrings are tape-wound shields.
 5. The shield of claim 1, wherein thethird and fourth annular rings each comprises the magnetically permeablematerial.
 6. The shield of claim 1, wherein the magnetically permeablematerial comprises Supermalloy, Metglas, Ultraperm, MuMETAL, or anycombination thereof.
 7. A system, comprising: a housing having a firstcavity and a second cavity; a current sensor disposed in the firstcavity; a calibration circuit disposed in the second cavity, wherein thecalibration circuit is configured to adjust phase and sensitivityproperties of a measurement output by the current sensor; and a set ofshields disposed within the first cavity of the housing about thecurrent sensor, wherein the set of shields comprises first and secondshields disposed on axially opposite sides of the current sensor, andthird and fourth shields disposed on radially opposite sides of thecurrent sensor, wherein each of the set of shields comprisesmagnetically permeable material, and wherein the housing is configuredto enclose the set of shields.
 8. The system of claim 7, wherein thefirst and second shields comprise first and second annular rings,respectively.
 9. The system of claim 7, wherein the third and fourthshields comprise third and fourth annular rings, respectively.
 10. Thesystem of system of claim 7, wherein the first and second shields eachoverlap both the third and fourth shields.
 11. The system of claim 7,wherein the set of shields is removably disposed within the housing. 12.The system of claim 7, wherein the housing comprises: a housing portionhaving an inner wall disposed circumferentially about a central opening,an outer wall disposed circumferentially about the inner wall, and abase extending between the inner and out walls; and a lid portionremovably coupled to the housing portion by one or more fasteners. 13.The system of claim 7, wherein the first and third shields comprise asingle piece.
 14. The system of claim 7, wherein the first, third, andfourth shields comprise a single piece.
 15. The system of claim 7,wherein the second cavity is disposed adjacent to the first cavity, andwherein the calibration circuit is configured to be placed adjacent tothe set of shields when the set of shields is disposed within the firstcavity.
 16. A method, comprising: absorbing at least one of electricaland magnetic interference with a set of shields disposed about a currentsensor, wherein the set of shields comprises: first and second shieldsdisposed on axially opposite sides of the current sensor; third andfourth shields disposed on radially opposite sides of the currentsensor, wherein each of the set of shields comprises magneticallypermeable material; and calibrating the current sensor via a calibrationcircuit disposed within a housing configured to enclose the set ofshields by adjusting phase and sensitivity properties of a currentmeasurement output by the current sensor.
 17. The method of claim 16,wherein calibrating the current sensor comprises: receiving an expectedmeasurement output that corresponds to the current sensor, wherein theexpected measurement output comprises expected phase and sensitivityproperties; sending a signal to a current source to provide a current toa conductor monitored by the current sensor; receiving the currentmeasurement output from the current sensor, wherein the currentmeasurement output comprises current phase and sensitivity properties;and adjusting the current phase and sensitivity properties tosubstantially match the expected phase and sensitivity properties.